1 University of Nebraska - Lincoln of Nebraska - Lincoln Historical Research Bulletins of the Nebraska Agricultural Experiment Station ( ) Agricultural Research Division of IANR Some Factors Affecting the Cooking Quality of the Pea and Great Northern Types of Dry Beans Edna B. Snyder Follow this and additional works at: Part of the Agriculture Commons, Food Chemistry Commons, and the Food Processing Commons Snyder, Edna B., "Some Factors Affecting the Cooking Quality of the Pea and Great Northern Types of Dry Beans" (1936). Historical Research Bulletins of the Nebraska Agricultural Experiment Station ( ) This Article is brought to you for free and open access by the Agricultural Research Division of IANR at of Nebraska - Lincoln. It has been accepted for inclusion in Historical Research Bulletins of the Nebraska Agricultural Experiment Station ( ) by an authorized administrator of of Nebraska - Lincoln.
2 COLLEGE OF AGRICULTURE UNIVERSITY OF NEBRASKA AGRICULTURAL EXPERIMENT STATION RESEARCH BULLETIN 85 Some Factors Affecting the Cooking Quality of the Pea and Great Northern Types of Dry Beans Edna B. Snyder Department of Home Economics IJNCOLN,NEBRASKA OCTOBER, 1936 I\.,,,. ' I.: ';. II'''\ r p<::n,...,..,,,.,,,-,, '...
4 COLLEGE OF AGRICULTURE UNIVERSITY OF NEBRASKA AGRICULTURAL EXPERIMENT STATION RESEARCH BULLETIN 85 Some Factors Affecting the Cooking Quality of the Pea and Great Northern Types of Dry Beans Edna B. Snyder Department of Home Economics LINCOLN, NEBRASKA OCTOBER, 1936
6 Summary Introduction CONTENTS Economic Importance and Geographical Distribution of Beans. Purpose of the Study. Preliminary Studies Soaking Methods of cooking. Experimental Methods and Results. Effects of scarification. Effects of size Effects of age and storage. Effects of deterioration. Effects of chemical solutions. Acid solutions. Neutral salts Sodium bicarbonate PAGE Sugar solutions Pectic solvents Practical Studies Discussion of Results
7 SUMMARY Dry beans of the Great Northern and pea-bean type from Nebraska and several other bean-producing states were studied to determine the factors affecting the cooking quality. A standard cooking procedure with distilled water was used to disclose differences in cooking quality, and th e percentage of beans too hard for table use was determined for each cooked portion. The factors studied were: soaking, including time and temperatures; storage, including time and storage conditions; age; size; place of origin; effect of chemical solutions; and the composition of the seed coat. The chemical solutions used were hydrochloric and acetic acids in different concentrations; sulphates and chlorides of calcium, magnesium, and sodium; sodium bicarbonate; and ammonium salts of oxalic, citric, and tartaric acids. A quantitative analysis of the bean seed coats was made for the following constituents: protein, fats, calcium, magnesium, and pectic material. Results of the study are as follows: 1. The cooking quality of the pea and Great Northern beans appears to be determined almost wholly by: (1) the structure and composition of the seed coat, which may be inherentl y hard, may have beco me hard as a result of environmental conditions, or mav have been hardened by chemical solutions; and (2) by the hygroscopic quality of the micropyle and germinal area. 2. Conclusions regarding the factors which modify or have a nega tive effect on cooking quality are as follows: (1) Beans cook more rapidly if soaked previous to cooking. The optimum soaking temperature appears to be around 120 F., and th e beans imbibe their own weight of water in five or six hours. A longer time is required if soaking is done at a lower temperature. (2) The cotyledons of all beans giving no evidence of sclerema become soft when the seed coats are scarified previous to soa king. (3) An optimum storage condition appears to consist of storage in tightly closed containers held at a temperature in the neighborhood of 45 F. Age alone apparently does not produce a hard-shelled condition. ( 4) Size is apparently a negligible factor in cooking quality. (5) Difference in place of origin did not contribute marked differences in cooking quality of the beans studied. (6) Solutions of hydrochloric and acetic acid in concentrations of 0.33 normal, 0.1 normal, 0.03 normal, and 0.01 normal depress water absorption and harden the seed coats of beans. (7) Solutions of sulphates and chlorides of calcium and magnesium in concentrations of 100 ppm depress water absorption and harden the seed coats of beans, and the hardness increases with increase of concentration of solutions. Solutions of sulphates and chlorides of sodium and potassium have no deleterious effect. (8) Solutions of sodium bicarbonate tend to soften the seed coats of beans and can be used effectively in amounts which are not deleterious to appearance or flavor. (9) Solutions of ammonium salts of oxalic, citric, and tartaric acid soften the seed coats of beans, that of oxalic being most efficient. (10) The seed coats of the beans studied contained relatively large amounts of pectic materials (which appeared in the form of pectic acid or pectates), and calcium, and slight amounts of protein, magnesium, and fatty materials. The Great Northern type analyzed in this study contained about twice the amount of calcium found in the pea bean. Results from cooking and from chemical analysis indicate that the pectic material may be effective in preventing entrance of water into the bean. (11) Practical baking studies show little justification for the excessively long baking time recommended by conventional recipes.
8 Some Factors Affecting the Cooking Quality of the Pea and Great Northern Types of Dry Beans EDNA B. SNYDER 1 Beans have occupied an important place as a world food, dating back to the ancients. Their use has been more general in southern European and Asiatic countries than on this continent and they still serve as the chief source of protein in many old-world countries, especially among the peasant classes. Because of their lack of cystine they are considered inadequate when used alone to supply protein; however, they do serve to supplement other more expensive nitrogenous foods and to add pleasing variety to the diet. Aside from their protein content, beans contain a high percentage of carbohydrate, are relatively rich in calcium, phosphorus, and iron, and contain magnesium as well as vitamins A and B. ECONOMIC IMPORTANCE AND GEOGRAPHICAL DISTRIBUTION OF BEANS Beans constitute a leading crop in a number of states and are constantly increasing in economic importance. Reports of the Federal Bureau of Agricultural Economics in recent years show marked yearly increases in bean consumption in the United States. States leading in dry-bean production are Michigan, New York, Colorado, New Mexico, California, and Idaho. Michigan leads in total yield and Idaho and California in acre yield. They are becoming an important crop in Nebraska. The types of white dry beans most generally grown for marketing purposes are the small, round pea bean and the large kidney-shaped bean known as the Great Northern. Both types probably originated in Chile and belong botanically to the species Phaseolus vulgaris. The pea-bean type is grown in Michigan and localities farther east, while the Great Northern seems to be generally better adapted to the states west of Michigan. Several of the larger commercial canners specify the smaller bean for their products and in certain localities there appears to be a definite preference among consumers for this type. On the other hand, in certain other localities canners and consumers alike express a definite preference for the larger bean. Reasons for preferences appear rather vague. One canner states that his choice of the pea bean is due to the fact that the shape is retained during processing. It is probable that habitual use of one type due to local production and prevalence in local markets has been the chief factor in developing preference. PURPOSE OF THE STUDY It has been generally observed that the cooking of dry beans has presented difficulty because of the variation in their capacity to become soft. This variation was observed by the Greeks as far back as 300 B. C. 1 The writer wishes to acknowledge suggestions and critic isms from Professors J. C. Russel and M. n. Weldon of rhe Department of Agronomy. and M. J. Rli sh of rhe Department of Agricuitural Chemist ry.
9 6 NEBRASKA AGRL. EXP.STATION RESEARCH BULLETIN 85 As a result, wide variation in cooking quality occurs even in the same lot of beans. There are frequently beans with seed coats which remain hard and prevent the entrance of water to the inside even after being cooked in boiling water. Such protection of the embryo tends to insure the germination of a portion of the seeds from any one plant. The purpose of this study was to investigate: ( 1) various factors either inherent or a result of environment which conceivably might affect the cooking quality of the pea and Great Northern types of beans; and (2) procedures to modify these factors. Factors which were considered were: ( 1) place of origin, (2) size, ( 3) age and storage conditions, ( 4) structure and composition of the seed coat, and (5) deterioration. Modifying procedures were: ( 1) soaking, including duration and temperature of water, (2) method of cooking, that is, boiling over direct heat, double boiler, pressure, and baking, and ( 3) effect of chemical solutions. The beans used for the study, together with their cultural histories, were secured from several important bean-producing states and from western Nebraska. 2 PRELIMINARY STUDIES It is at once evident that a procedure for cooking dry beans must provide for the imbibition of a relatively large amount of water both by the seed coat and the cotyledons. Any treatment tending to lessen the imbibition of water would obviously be detrimental to the cooking process and to the quality of the resulting product. As a preliminary step to the study it was necessary to study some of the factors listed above as probably affecting cooking quality in order that a cooking procedure, satisfactory for use in disclosing differences in quality of beans from different lots, could be developed for use in the laboratory. The preliminary study consisted of experimentation with various lots of beans, methods of soaking, kinds of water ( such as tap and distilled water), and methods of cooking ( such as boiling directly over heat, double boiler, and pressure). Soaking.-To eliminate any effect from mineral present in the water, distilled water was used for both soaking and cooking the beans which were to be compared. Preliminary study, shown in Figure 1, showed that in general the beans absorbed their own weight in water in from fi ve to six hours, provided the temperature of the water was considerably above room temperature. There was little increase in weight by longer soaking, and cooking time was not reduced. A lower soaking temperature required a longer time for the same result. The five-hour soaking period was well adapted to a laboratory schedule and should be practical in household use. The cooked beans which had been soaked were more pleasing in appearance, appeared lighter in color, and were more evenly cooked than 2 The out-of-state bea ns used in this study were fu rn is hed by experi ment stat ions in the fo llow ing states: Michigan, Colo rad o, Idaho, and Monta na. The Nebras ka beans were fu rn ished by Chester Brown of Gering and Morrill, Nebras ka, who obtained them from farmers in that loca li ty, and by C. W. Beebe of Va\ley county, who prod uced th e beans in sand- hill soil. Samples from two com mercial sources were also used.
10 COOKING QUALITY OF BEANS 7 those which had not been soaked. The cooking time was reduced considerably by soaking, but the weight of the cooked beans was the same whether soaked or not soaked. Methods of cooking.-lt was found that when the beans were cooked in rapidly boiling water they tended to lose shape and become mushy; similar results were obtained when they were cooked in a double boiler slightly below boiling temperature. Considerable experimental work was done with the pressure cooker to determine if this method would produce 18-r ~ ~11111~ (I) 14 w ~ GREAT NORTHERN (MONTANA) ----PEA BEAN (MICHIGAN) 8-r--, , , ,---' OVER NIGHT 15 HOURS FIG. 1.- Rates of imbibition of water by Michigan pea beans and Montana Great Northern beans. a more tender product in a shorter time than by ordinary boiling. Cooking for 30 minutes at 15 pounds pressure produced beans which were soft with tender seed coats, but were mushy and dark in color, with a flavor generally considered as undesirable. Cooking for 40 minutes with 10 pounds pressure produced a somewhat more desirable product, but still not meeting acceptable standards in appearance and flavor. Baking was eliminated as a method for comparing the quality of different lots of beans, because it is a more complicated procedure and difficult to standardize. However, attention was given to this method later in the study. EXPERIMENT AL METHODS AND RESULTS The soaking, cooking, and sorting procedures finally adopted were as follows: The beans from the different places of origin were selected so that all appeared edible. One hundred grams were soaked for five hours in 450 cubic centimeters of distilled water at approximately 120 F. The same water was used for both soaking and cooking, as the resulting flavor was considered less variable when the soaking water was retained for cooking. At the end of the soaking period the beans were drained and
11 8 NEBRASKA AGRL. EXP. STATION RESEARCH BuLLETIN 85 weighed. The water was heated to the boiling point and the beans added and allowed to cook one and one-fourth hours, or the minimum time found necessary to produce a tender, uniformly cooked product with the beans used in the study. The utensils used were pans of pressed aluminum so shaped that they could be used in triplicate on a single burner. They were two quarts in capacity with tightly fitting lids held by clamps. The type of pan described was selected so that a greater number of portions could be cooked at the same time. The beans were cooked on a 1,000-watt electric unit, kept on "low" throughout the cooking period to prevent rapid boiling. The beans were cooked without salt, as the presence of salt appeared to mask or change the flavor. After cooking, the beans were again drained and weighed, and compared while still warm. Since tenderness of both seed coat and cotyledons is an important criterion for comparison of cooked beans, that characteristic was used as a basis of comparison and was supplemented with subjective ratings for flavor. Several mechanical methods were tried for measuring tenderness but were abandoned because of difficulty in obtaining comparable measurements. The methods tried consisted of puncturing, cutting, and crushing the beans and measuring the amount of pressure necessary to do the work. It is not possible to standardize a bean as to size and shape as may be done with a cut vegetable. As a result of the swelling of the bean, the cotyledons when cooked tend to separate, leaving a space between. Measurements are complicated because the resistance of the seed coat may be greater than that of the cotyledon, making it uncertain which resistance is being measured. When considering the cooking quality of the beans, slight variations in hardness are not important factors, but whether or not they are suitable for table use is important. Because of the above difficulties, a hand method was used for comparing the tenderness of cooked beans. It is conceded at the outset that the method chosen will be open to criticism, because it is not entirely objective. However, it provided a more satisfactory basis for comparing different lots of beans than the mechanical methods tried. Frequently when a mechanical method is used for measuring tenderness of food products, it is justified on the grounds that it agrees with hand sorting. The procedure used in this study was as follows: Each quantity of cooked beans was sorted by hand into two portions---one portion made up of those beans which were sufficiently soft for table use and another portion of those too hard for table use. Testing was done by puncturing each bean by hand with a No. 5 sewing needle. By this method the entire quantity of beans was checked and the percentage, by number, of hard beans was computed. The wide variation in the characteristics of beans, even from the same lot, has been mentioned; no two samples of equal weight are identical in characteristics. Because of this lack of uniformity, results from cooking different quantities are quite likely to show wide differences, and it is impossible to duplicate results. Therefore in experimental work of this
12 CooKING Q UALITY OF BEANS 9 character a high degree of precision is impossible, and conclusions must necessarily be drawn from a large number of trials. In Table 1 is shown a comparison of the different lots of beans from the various places of origin when cooked by the standard procedure. All but one lot, which was received later during the study, were from the 1933 crop. The table includes the percentage gain in weight after soaking and after cooking and gives the percentage of hard beans, or those not sufficiently soft for table use, at the end of the cooking period. The TABLE!.-Percentage gain in weight of 100 grams of beans from soaking and cooking and percentage of beans unsuitable for table use. 1 Gai n in wt. I Gain in wt. I T ype Michigan (1) Idaho Monta na Colorado Commercial Fancy "Fernald" Idaho Commercial Mich. Bean Growers Michigan (2) Nebr. E'xp. Sta. plot Nebr. No. 1 Nebr. No. 2 Nebr. No. 3 Nebr. No. 4 Nebr. No. 5 Nebr. No. 6 Nebr. No. 7 Nebr. No. 8 Nebr. No. 9 Source 2 Pea bean Great Northern Great Northern Pea bean Great Northern Pea bean Pea bean Great Northern Great Northern Great Northern Great Northern Great Northern Great Northern Great Northern Great Northern Great Northern Pea bean Moisture content I from soaking from cooking Unsuitable for tab le use Bea ns were cooked when fi rst received. The percentage of hard beans was ca lculated from the number of beans. 2 All of the beans studied were from the 1933 crop except those from Michigan (2). 3 The moisture content was determined by drying to constant weight in a vacuum oven. place of origin did not appear to be a significant factor in cooking quality, with the beans studied. Differences in the percentages of hard beans were small among lots of out-of-state beans. There were somewhat greater differences among the different lots of Nebraska beans. However, in several lots of the latter there were a large number of broken seed coats, so that differences in weights or tenderness have little significance. In general, the beans grown in Nebraska compared favorably with those from other states. These results do not show a significant relation between cooking quality and moisture content. In the different lots grown in Nebraska there is generally a slightly lower percentage of hard beans with the higher moisture content, but again other factors such as breaks in the seed coat may account for this. The beans of the pea type in all cases maintained
13 10 NEBRASKA AGRL. ExP. STATION RESEARCH BuLLETIN 85 their form during cooking somewhat better than did the Great Northern, because the seed coat of the former tends to remain intact. It is realized that a study of food flavor is subjective in nature and that it is difficult or impossible to set standards. Opinions of food quality vary widely and are conditioned by previous customs and habits. A committee made up of members of the Home Economics faculty served as judges of the characteristics of the beans listed in Table 1. Very little preference was expressed for any particular lot of beans. They were all rated as desirable. The pea-type bean was characterized in some cases as being more pronounced or "nutty" in flavor, while the Great Northern was considered as slightly bland or neutral. In only a few cases were the seed coats designated as tough or hard, and such designations were about equally divided for the two types. Those of both types rated as most pleasing in flavor were grown in the sand hills of Nebraska under the same cultural conditions. Most of the beans were desirable in texture. Those which were poorest in texture were grown in a Nebraska Experiment Station plot in both fertilized and unfertilized soil. The beans were tender but mushy in appearance. Generally, beans which did not become sufficiently soft for table use after cooking one and one-fourth hours, responded to longer cooking. A small percentage passed through both soaking and cooking processes without imbibing water but invariably became soft after the seed coat was scarified, making it possible for water to enter. The above results are of interest in view of the fact that A. de Dominicis 3 states that the capacity of legumes to soften is not dependent upon the outer integuments, but upon the imbibition of water by the colloidal forms which make up the beans, the amount depending upon their previous history or their degree of reversibility. EFFECTS OF SCARIFICATION Because of the apparent importance of the nature of the seed coat as it affected the entrance of water, some study was made of the effects of skin scarification. Beans were selected from the same lot, one portion containing only those with coverings which appeared visually to be intact, and the other containing beans with scarified seed coats. Samples from various lots were used. It was found that when cooked by the standard method, both the soaked and cooked weights of the scarified beans were somewhat higher than those with the covering intact. With beans which cooked relatively well the cooking time was reduced 40 per cent by this treatment, but of course the appearance was less desirable. Scarification has been used considerably as an aid to germination of legume seeds, but has probably not been considered as an aid to cooking. Since scarification proved an effectual method as an aid to cooking beans, the importance of the imbibition of water by the seed coat appeared to warrant further study. It should not be assumed that the entrance of water into seeds is uniform over the entire surface. Studies have been 3 A. de Dominicis, Ann. Scuola Agr. Portici 16,3 1 (1 920), Chem. Abs. 17,3388 ( 1923).
14 COOKING QUALITY OF BEANS 11 made which show that at least in some seeds, the entrance of water at ordinary temperatures is largely through the micropyle and germinal area, which are hygroscopic. The seed coat of beans appears to be rather loosely attached to the cotyledons with a cement-like substance holding it to them. Observations of beans during soaking show that the germinal area swells first, indicating the entrance of water by this route. The water passes around the periphery of the bean, causing the seed coat to become wrinkled. Gradually the inside of the bean swells and the wrinkles disappear. The swelling of the embryo tends to loosen the seed coat from the hilar groove, thus providing an opening for water. Water enters freely through breaks occurring in the covering. The path of a liquid into the bean can be traced by soaking in iodine and observing the blue color. To verify the localized entry of water into the beans, the following process was used: The micropyle and area near it (Great Northern type) were blocked with melted beeswax. Each bean was weighed before and after blocking. An equal number of control beans were likewise weighed. Both lots were soaked in distilled water at room temperature for 24 hours. At the end of the soaking period they were again weighed. From the lot with germinal areas blocked, the average gain was only 0.28 per cent, while for the controls it was 79. The experiment was repeated with bicycle-tire cement as a seal, as the latter formed a thin coating less likely than beeswax to break loose from the bean. Results were similar to those with beeswax. The percentage gain in weight for the beans blocked with cement was 3.8, while for the controls it was 52 per cent. A larger percentage of beans of the pea type swelled with the germinal areas blocked, a result which might possibly indicate a more general permeability of seed-coat surface. It is admitted that these results can not be considered as precise. Among the controls with no seal to prevent entrance of water were several beans which remained hard and it is probable that a number of the beans with the germinal area blocked would have remained hard without the seal. Apparently the micropyle is not always hygroscopic, and results from cooking show that occasionally even cooking at boiling temperature is without effect. Results do, however, point to the generally localized entry of water into the beans, and suggests the importance of further information regarding the structure and composition of the seed coat. EFFECTS OF SIZE To determine if size is a factor in cooking quality, beans from the same lot were sorted into two portions according to size; samples were selected from various lots, and cooked by the standard method. Results from the different lots were not consistent. From some lots the small and large beans cooked equally well, while in others there was a decided advantage in favor of the large beans. In general the beans which appeared well matured cooked most readily. A comparison of the two types shows that the Great Northern cooks as quickly as the pea type, even though the beans are considerably larger in size.
15 12 NEBRASK A A GRL. ExP. STATION R ESEARCH B u LLETIN 85 EFFECTS OF AGE AND STORAGE Even though beans cook well when first matured, certain successive environmental conditions appear to affect their cooking quality. There appears to be a popular idea that all old beans are difficult to cook. Instances are well known in which bea ns which originally cooked well have become very difficult to cook after storage. Such an instance occurred in the Department of Home Economics. Beans stored under laboratory conditions of temperature and moisture became so hard that they could not be cooked satisfactorily. Beans stored in tin containers in the research laboratory near the steam pipes, likewise became hard. Similar results were obtained by drying beans in an oven at a temperature of 100 F. Laboratory temperatures range from 70 to 80 F. and the humidity is generally low. To determine the effects of storage at fairly constant temperatures, samples from various lots were stored in tightly closed glass jars with rubbers, a part of them at 72 to 80 F. and a part at approximately 45 F. Results are shown in T able 2. T ABLE 2.- Effects of 15 to 17 m onths storage at temperatures of 45 and 76 F. on 100 grams of beans. Source I :Elrfr without storage Idaho Great Northern. 90 Montana Great Northern. 88 Michigan pea beans 86 Nebr. Exp. Sta. Great Northern. 99 Nebraska No. I. 85 Nebraska No Nebraska No Nebraska No Nebraska No Nebraska No Nebraska No Nebraska No I Gain in wt. from cooking without storage Hard beans JO 0 17 Gain in wt. from soaking after storage Gain in wt. from cooking after storage Hard beans JO Mean storage temp. Deg. F The table shows that under the conditions stated the cooking quality of the beans was not impaired and was even superior to that before storage. The imbibition of water after storage was somewhat greater than before. Those stored at 45 F. were most desirable. These results show that age alone is not a factor in producing hardness but where hardness results, the condition is probably related to temperature and humidity. A relatively
16 COOKING Q UALITY OF BEANS 13 low temperature (not above 50 F.) with conditions that prevent or reduce loss of moisture probably offers the optimum storage condition. EFFECTS OF DETERIORATION Several lots of beans of the navy variety were received from a local cannery with the report that they could not be softened satisfactorily for canning. The reaction of the beans suggested to the canners the possibility of their having been treated with lime previous to shipment. It was found that a large percentage of the beans became soft, but out of each lot there was a sufficient number of hard beans to give the effect of underprocessing. Chemical examination failed to disclose any presence of lime. The hardness was not confined to the seed coats; the entire bean resisted cooking. The hard beans were noticeably darker in color than those which became tender. Various treatments were used in an effort to soften the hard beans but none was entirely satisfactory. From another source beans were obtained which were known to be fourteen years old. These beans were likewise dark in color and remained hard throughout various treatments. They gained weight in soaking and cooking but did not become soft. Their moisture content was as high as that of some other beans which softened readily. It is probable that this type of hardness is a result of adverse temperature and moisture conditions in the field during harvesting or during storage, and is undoubtedly that known as "sclerema", which is produced from enzymatic changes resulting from storage in damp atmosphere at high temperature with no ventilation. Gloyer states that sclerema is not a matter of age alone, as it can be produced artificially in ten days. 4 EFFECTS OF CHEMICAL SOLUTIONS The results of the experimental work described above show that the long cooking period commonly used for beans is necessary largely for the purpose of softening the seed coat. Beans with seed coats removed and without evidence of sclerema became tender when cooked from 30 to 45 minutes. Since the softening of the cotyledons appeared to depend upon the imbibition of water, the limiting factor being the seed coat, the problem resolved itself into one of treatment which could be used safely to increase permeability and to hasten the softening of the latter. Such treatment would be advantageous from the standpoint of both economy and palatability. On the other hand, it was possible that certain treatments might result in actual hardening of the seed coat, thereby preventing the imbibition of water and causing the product to be less palatable. Little detailed information seems available concerning the composition of the seed coats of beans. Reported chemical analyses of beans consist of the composition of the entire bean. Considerable microchemical study has been made of the structure of seed coats of legumes and other seeds but such study has been from the standpoint of germination. Statements are 4 W. 0. Gloyer, Sclerema and hard shell, two types of hardness of the bean, Proc. Assoc. Offic. Seed Analys ts of North America, pp. I1 21, 1921.
17 14 NEBRASKA AGRL. ExP. STATION R ESEARCH BULLETIN 85 numerous relative to the digestibility of beans-the low coefficient of digestibility being attributed to the "insoluble" materials found in the seed coats. The constituents of seed coats have generally been believed to include complex carbohydrates in the form of celluloses and hemicelluloses in combination with pectic substances, with possibly some cutin, lignins, tannins, and various fatty and waxy substances. There appears to be still a question as to whether or not some of these combinations are chemical or merely physical. Because of the complexity of seed-coat structure and composition and the lack of definite information, a theoretical selection of solvents was difficult. An empirical procedure was therefore followed in this study to determine the effect of various solutions on the beans. The solutions used were: (1) acids, (2) neutral salts, (3) sodium bicarbonate, and ( 4) solvents for pectic substances. Acid solutions.-because of the effect on imbibition of water from breaks in the seed coats of the beans, a portion of those used for the acid studies were selected so that they were free from visible breaks. For the first acid studies, twenty grams of beans, which were weighed on a Chainomatic balance, were used. The beans were soaked for five hours at a temperature of 120 F. Two variations in procedure followed the soaking. In one the beans were washed with, and cooked in, distilled water. In the other the solution was neutralized with 3.-Effect of acids on imbibition of TABLE sodium bicarbonate and the 20 grams of Great Northern beansaverage of three trials with soaking at beans cooked in the neutralized solution. The acids chosen 120 F. Gain in were hydrochloric, representing an inorganic acid and one I Gain in I Acid Normality wt. w hen wt. when soaked cooked having a high degree of ionization, and acetic, represent Hydrochloric Hydrochloric ing an organic acid and one Hydrochloric having a low degree of ionization. The acids were used in the following concentrations: 0.33 normal, 0.10 normal, 0.03 normal, 0.01 normal. Controls w i t h distilled water were used for comparison. Typical results are shown in Table 3. The table shows that the acids tended to de Hydroch loric Hydrochloric Hy.drochloric Acetic Acetic Acetic Acetic Acetic Acetic Disti lled water Cooked in distilled water. 2 Cooked in soaking solution neutralized with sodium bicarbona te. press the imbibition of water and the depression generally increased with increased strength of acid. The effect on the beans of the 0.01 normal acid was slight, but the seed coats were very tough with the 0.33 normal
18 TABLE 4.-Effect of acids on 100 grams of beans selected without visual breaks in the seed coatsaverage of three trials. Pea beans Acid Normality I G:-iin in Cain in weight weight Results soaked cooked P. Cl. Hydrochloric Very lurd, coats intact Hydroch loric Hard, coats imact H ydrochloric J\t\orc like control Hydrochloric Coats loose, cotyledons very soft H ydrochloric H ard Hydrochloric More like control Acetic Very hard, coats intact Acetic H:i rd coats, intact Acetic Similar to control Acetic Very hard, disagreeable fla vo r Acetic Softer than above Acetic Similar to co ntrol Distil led wa.ter Soft 1 Cooked in distilled water. 2 Cooked in soaking solution neutralized with sodium b icarbonate. Gain in weigh t soaked Gain in weight cooked P. ct Great Northern Res ults Coats very ha rd, many loose Coats hard, beans soft Si milar to control Co;its loose, fl avor a nd appearance undesirable Coats loose, fl avor and appearance undesi ra ble Similar to control Very hard H ard Similar to cont rol Mushy, coats loose, tough, undesi rable Softer than above Simi lar to control Soft TABLE 5.-Effect of acids on 100 grams of beans selected without regard to breaks in the seed coatsaverage of three trials. 1 Pea beans Great Northern G:1in in Ga in in Gain in Gain in Ac id Normality weight weight Results weight weight Results soa ked cooked soaked cooked P. ct. P. Cl. P. ct. Hydrochloric 0.33 Coats very tough Coats tough, loosened, beans soft Hydrochloric I Coats very tough Coats tough Hydrochlori c Coats tough Coats tough Hydrochloric Similar to control Similar to control Acetic Coats ve ry tough Acetic Coats tough Coats ve r y tough Acetic Coats tough Acetic 0.01! Similar to control Similar to control Distilled water Soft Soft 1 Before cooking, the acid soaking so lutio ns were neutralized with NaHC03, and the beans were drained and cook ed in disti lled wa ter. Q 0 ~ z <:l to d :,. r" ~ 0 "1 ttl t,j :,. z "' -Vl
19 16 NEBRASKA AGRL. EXP. STATION RESEARCH BULLETIN 85 acid. The interiors of the beans were soft but they gave the appearance of being hard because of the hard coverings. Acetic acid appeared to produce a tougher seed coat than did hydrochloric. The beans cooked in the neutralized solutions were more broken and less desirable in appearance than those which had been washed and cooked in distilled water. Following the study with 20-gram weights of beans, 100 grams were used, as a greater weight of beans should be more representative of any one lot. The same procedure as described above was used. Results are shown in Table 4. The results in Table 4 are similar to those in Table 3. There is shown the same general trend of depressed imbibition of water with the acids and the same toughness of the seed coat. Further studies were made of the effects of acids on beans selected without regard to breaks in the seed coats. The soaking procedure was the same as that reported in the previous acid studies, but differed in that the soaking solution and beans were neutralized with sodium bicarbonate, the beans washed with distilled water, and cooked in distilled water. Typical results are shown in Table 5. While the variations are less consistent than with the more carefully selected beans, there are similar general tendencies, and in no case were results as desirable as with the control. Tests were made with beans of both types-from various sources and various lots. While there were wide variations in soaked and cooked weights of beans from different lots, the same general relative trends were shown from results with the acids as compared with the controls. Since the preceding studies indicated that for the procedures used the hardening effect of the acid treatment was on the seed coats only, further verification appeared advisable. To determine the effect of the acid solutions on the cotyledons of the beans, the seed coats were removed. Twenty grams of bean cotyledons were soaked and cooked in the acid solutions. The beans were cooked in earthen containers in the oven to prevent complications from the action of acid on aluminum. Controls were soaked and cooked in distilled water. Results are shown in Table 6. The beans which were soaked and cooked in the hydrochloric acid solutions were very soft, becoming gelatinous on standing. Those in acetic acid solutions were less soft than in hydrochloric, and the form of the bean was retained. Longer cooking increased the tenderness of the beans cooked in acetic acid. The controls were cooked to pulp. Table 6 shows that for both the controls and the acid-treated bean cotyledons, the percentage gain in weight was higher at room temperature than at 120 F. Reference to Figure 1 shows that beans with seed coats intact absorbed water more rapidly at a temperature of 120 F. than at lower temperatures. The percentage gain in weight from soaking of the controls as compared with the acid treated bean cotyledons was less than that shown in Table 3 where the entire bean was used. A few checks with 0.33 normal oxalic acid as the soaking solution showed that the effects of this acid were dissimilar to those of acetic and hydrochloric acids. Water imbibition was not depressed and the seed coats
20 COOKINGQUALITY OF BEANS 17 TABLE 6.-Effects of acids on 20 grams of cotyledons of Great Northern beans-average of three trials. Acid Normality J Temperature I Gain in wt. Result for soaking when soaked when cooked Deg. F. Hydrochloric Could not weigh 75 to Very soft Hydrochloric Very soft 75 to Very soft Hydrochloric Very soft 75 to Very soft Acetic Less soft than in HCl 75 to Less soft than in HCl Acetic Less soft than in HCI 75 to Less soft than in HCl Acetic O.Ql Less soft than in HCl 75 to Less soft than in HCI Control, distilled water Pulp 75 to Pulp did not appear as hard in the latter. Obviously the use of this acid would be impossible in the preparation of an edible product, but the results suggest further investigation because of the possibility that calcium salts are present. Oxalic acid renders calcium insoluble, while hydrochloric would be expected to attack it. TABLE 7.-Analyses of natural hard waters. Nature of hardness I Western I Manhattan, I Edgemont, Blair, I Marshall Co., Springs, Ill. Kans. S. Dak. Nebr. Kans. Temporary hardness (alkalinity) Permanent hardness Total hard nessas calcium carbonate per million Total hardnessas milli equivalents per liter Calcium, milli.equivalents per liter Magnesium (by difference) Chloride Trace Medium Large Trace Sulphate.... Large Trace Medium None Neutral salts.- lt has been observed that in certain localities the cooking of beans is attended by difficulties which appear to be related to the water. Waters vary in the kind and amount of mineral salts which they contain. Some waters contain only temporary hardness in the form of calcium or magnesium bicarbonate, which can be removed by boiling (precipitated as carbonate), while some contain sulphates and chlorides of magnesium and calcium which cannot be removed by boiling. The latter are known as permanently hard waters. There appears to be considerable disagreement as to the nature of the action of hard water on beans. Statements have been made to the effect that calcium and magnesium sulphates unite with the protein legumin to form insoluble compounds.
21 18 NEBRASKA AGRL. ExP. STATION RESEARCH BuLLETIN 85 To obtain information as to the effects of water containing mineral salts, the following studies were made. Excessively hard waters were obtained from different localities, and were analyzed chemically. Beans were soaked in the different hard waters and then cooked in the same water by the standard procedure. Beans which had cooked well in distilled water were used for the hard-water studies and were from the same lots. Tap water ( Agricultural College Campus), which contains temporary hardness, was also used. Results are shown in Table 8. The table shows that for each water used, there resulted a depression in imbibition and a high percentage of hard beans, in one case as high as 100 per cent. The percentage of hard beans increased as the soaked weights decreased. The seed coats in all cases were less tender than those of the controls. Those cooked in the tap water were similar to the controls. A comparison of Tables 7 and 8 shows that as the permanent hardness of the water increased, the percentage of hard beans tended to increase. To determine the kind and amount of mineral which may be detrimental to cooking, standard solutions of calcium and magnesium sulphates and chlorides in concentrations equivalent to 2,000, 1,000, 500, 250, and 100 parts per million of calcium carbonate were used for cooking beans, and results compared with those when distilled water was used. In these TABLE 8.-Effects of natural hard waters on imbibition of 100 grams of beans-average of three trials. Wa ter u~ed I Wt. when Wt. when Hard soaked cooked beans Pea beans I Grams Grams Tap water, Nebr. Agrl. College Manhattan, Kans Blair, Nebr Edgemont, s. Dak Weslern Springs, Ill Marshall County, Kan s Distilled water Great Northern beans Tap water, Nebr. Ag rl. Co llege Manhattan, Kans Blair, 1cbr Edgemont, s. Dak Western Springs, Ill Marshal l County, Kans studies, beans were selected Distilled water first without regard to breaks in the seed coat, and were from the same lots. Both varieties were grown under the same cultural conditions. The standard soaking and cooking procedure was used, except that the beans were soaked and cooked in the salt solutions. Typical results are shown in Table 9. In all cases the depression of water absorption increased as the concentration of the solution increased. Solutions of calcium salts produced a somewhat more pronounced hardness than did those of magnesium, and there was little difference between concentrations of 2,000 and 1,000 ppm. There was also less tendency for the seed coats to loosen in the calcium solutions. Solutions of either salt in concentrations of 2,000 ppm produced beans almost as hard as uncooked beans. Solutions of the same salts seemed equally
22 COOKING QUALITY OF BEANS 19 TABLE 9.-Effect of standard hard waters on imbibition of 100 grams of beans selected without regard to breaks in seed coats. Solution Pea beans - Great Northern beans Gain in Gain in Gain in Gain in weight weight Hard we ight weight Hard soa ked cooked beans soaked cooked beans I I P. ct. />. ct. P. ct. Calcium ch loride 2,000 ppm ,000 ppm ppm 83 Ill Seed coats tou gh Seed coats tough. In sid es soft. Insides fai rl y 250 ppm Less tough. soft. 100 ppm Slightly tougher Less tough. than controls Slightly tou gher tha n controls. Calcium sulphate 2,000 ppm JOO 1,000 ppm ppm Seed coa ts tough Seed coats tough. Insides soft. Insides soft. 100 ppm Slightly tou gher tha n controls. Ma g nesium chloride 2,000 ppm ,000 ppm Slightly less Slightly less hard than above. tough than above. More broken than in calcium. 500 ppm Less tough than 250 ppm above. Less tough than above. 100 ppm More like controls. Ma g nesium sulphate 2,000 ppm ,000 ppm Slightly less Sli ghtly less hard th an above. tough than above. 500 ppm ppm ppm Distilled water I I effective whether as chlorides or sulphates. In the magnesium solutions in concentrations of 1,000 ppm the hardness was less perceptible than for 2,000 ppm. Longer cooking failed to soften the seed coats cooked in either sol ution. With concentrations of 500 ppm the hardness was less evident than in more concentrated solutions but was noticeably greater than for the controls. Following the above, further study was made using beans selected without visible breaks in the seed coat so that water uptake through breaks was reduced to the minimum. Typical results are shown in Table 10. The table shows the same tendencies but with greater consistency than those reported in Table 9, i.e., depressed imbibition and hardness of the seed coat. Again the effects from calcium appeared somewhat more pronounced than those from magnesium. To determine if the hardening effect from solutions of calcium and magnesium salts was on the seed coats alone, studies were made on the cotyledons of the beans as was done w ith the acid solutions. Twenty
23 20 NEBRASKA AGRL. ExP. STATION R ESEARCH B ULLETIN 85 grams were used. They were soaked and cooked in the various natural hard waters and in the standard solutions in concentrations of 2,000 ppm. For comparison, equal weights of whole beans were treated in the same way. The cotyledons were cooked into pulp with one exception, those cooked in water from Marshall county, Kansas. In the latter, the form was retained and the beans were relatively hard. Results from the standard solutions are shown in Table 11. The table shows that for the cotyledons alone the percentage gain in soaked weights is as high as that of the control. The controls were cooked into pulp and those in the magnesium solutions were very soft, while in the calcium solutions the beans were soft but TABLE 10.-Effect of standard hard water solutions on imbibition of 100 grams of beans selected without visual breaks in the seed coat- average of three trials. Pea beans Great Northern beans Solution Gai n in weight Gain in weight Soaked Cooked Soaked Cooked P. ct. Calcium chloride, 2,000 ppm ,000 ppm Calcium sulphate, 2,000 ppm ,000 p pm Magnesium chloride, 2,000 pp m ,000 ppm Magnesium sulphate, 2,000 ppm ,000 ppm Distilled water retained their form. They were similar in appearance to the beans cooked in acetic acid solutions. Comparison of percentage of gain in the soaked weights of the bean cotyledons with those of the whole beans shows the former to be considerably higher, indicating that the effect of the hard water is on the seed coat alone. Following the studies with calcium and magnesium salts, both salts of bivalent metals, studies were made to determine if the effects of solutions of sodium and potassium chloride, salts of monovalent metals, were similar. Results are shown in Table 12. There appeared to be no deleterious effects from either of the sodium or the potassium salts used ; the imbibition of water was somewhat improved and the seed coats were tender. Solutions of these salts at concentrations of 4,000 ppm, or double the maximum used for calcium and magnesium, were used with no observable effects. Since the effects upon the bean seed coats of the use of solutions of salts of bivalent and monovalent metals were dissimilar, information on the effects of a solution of aa salt of a trivalent metal was obtained. A